Anvil assemblies are typically employed in power tools (e.g., electrically-operated power tools, pneumatic power tools, etc.) to transfer torque from a motor to a tool element to perform work on a workpiece. Particularly, impact wrenches utilize anvil assemblies to transfer a striking rotational force, or intermittent applications of torque, to the tool element and workpiece. As such, impact wrenches are typically used to loosen or remove stuck fasteners (e.g., an automobile lug nut on an axle stud) that are otherwise not removable or very difficult to remove using hand tools.
Depending upon the size and configuration of the impact wrench, a relatively large amount of torque may be transferred through the anvil to the tool element and workpiece. Anvils typically include a square head configured to receive the tool element, and a shoulder against which the tool element is abutted. The shoulder is typically formed by a continuous or non-continuous surface extending substantially perpendicular to one or more flats on the square head. As such, a fillet having a relatively small radius is often employed to transition the respective flats on the square head to the shoulder on the anvil. Such small fillet radii, as a result of the high torsional loads that may be carried through the anvil, often yield an area of high stress at the base of the head.